server.js

const http = require("http");
const fs = require("fs");
const path = require("path");

const root = __dirname;
const port = Number(process.env.PORT || 3000);

const mimeTypes = {
  ".html": "text/html; charset=utf-8",
  ".json": "application/json; charset=utf-8",
  ".js": "text/javascript; charset=utf-8",
  ".css": "text/css; charset=utf-8",
  ".png": "image/png",
  ".jpg": "image/jpeg",
  ".jpeg": "image/jpeg",
  ".svg": "image/svg+xml",
  ".mp4": "video/mp4",
  ".wdp": "application/octet-stream"
};

function safePath(urlPath) {
  const decoded = decodeURIComponent(urlPath.split("?")[0]);
  const requested = decoded === "/" ? "/chatsim.html" : decoded;
  const fullPath = path.normalize(path.join(root, requested));
  return fullPath.startsWith(root) ? fullPath : null;
}

const server = http.createServer((req, res) => {
  const filePath = safePath(req.url || "/");
  if (!filePath) {
    res.writeHead(403);
    res.end("Forbidden");
    return;
  }

  fs.stat(filePath, (statErr, stats) => {
    if (statErr || !stats.isFile()) {
      res.writeHead(404);
      res.end("Not found");
      return;
    }

    const ext = path.extname(filePath).toLowerCase();
    res.writeHead(200, { "Content-Type": mimeTypes[ext] || "application/octet-stream" });
    fs.createReadStream(filePath).pipe(res);
  });
});

server.listen(port, () => {
  console.log(`ChatSim running at http://localhost:${port}/chatsim.html`);
});